Position indicating device



' June 8, 1943. HOLMES, JR" g- 2,321,386

POSITION INDEECATING DEVICE Filed Oct. 5, 1942 F 2. I. A MPLIFIER lnvehc'orsz Lowell L. Hclm'es Jru, Orrir'w W. LJvirlgsb'on,

. Thei s"- Attorne Patented June 8, 1943 PATENTY OFFiE POSITION INDIQATING DEVICE and Orrin W. Livingston,

Lowell L. Holmes, Jr.,

Scotia, N; 2.,

assignors to General Electric Comparty, a corporation of New York Application October' 5, 1942, Serial No. 460,888

' 16 Claims. (Cl. 33-125.)

Another aspect of the invention is the com bination of two edge position indicating devices arranged in proximity to opposite edges of an object of conducting material and connected so that the indications are algebraically added'to indicate the width and changes in width of the object.

Another object of the invention is the provision of an indicating device of the character described which may be used to indicate the position of an edge or the width ofa stationary object or of an object which moves from side to side in the direction of its width, or shifts up and down and which varies in thickness and in width, such for example as a hot strip of steel which is being reduced in a rolling mill. In this connection, the invention is particularly suited to the continuous measurement of the width of a moving web or strip.

Other objects of the invention are the provision of an indicating device of the character described which is rugged and ableto withstand considerable physical injury without impairment of its accuracy and which will not be damaged by excessive heat, or mechanical friction, and which will give an accurate indication irrespective of atmospheric conditions encountered in steel mill operation, such as smoke, scale, moisture, and dirt. In carrying the invention into effect in one form thereof, a movably mounted jet of electrical conducting fluid, such as water, is positioned near the edge of an object of electrical conducting material. Suitable driving means, such as an electric motor, are provided for moving the jet. A change in the position of the object with respect to the jet produces a change in-the electrical conductivity between thejet andthe object. This change in conductivity is utilized to control the driving means to move the jet to follow the change in position of the edge. An indicating device indicates the amount of movement of the jet from an initial position and thereby provides an indication of the position of the edge.

In illustrating the invention in one form thereof, it is shown as embodied in a system for indicating the width of a strip of hot steel.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing, in whioh'Fig. l is 'a simple, diagrammatical sketch of. an'embodiment of the invention and Fig. 2 is a detail of a modification.

. Referring now to the drawing, a strip of material it, such for example as a strip of hot steel, is being passed from one roll stand (not shown) of a rolling mill to a second roll stand thereof. I

This strip is moving in a direction which in the drawing is perpendicular to the plane of the drawing and is therefore shown in section.

For detecting and indicating -the position of the right edge of the stripdfi, a detecting and indicating unit is provided. This unit comprises means for projecting a pair of jets H and i2 of an electrical conducting fluid, such for example.v as water, in proximity to the edge of the strip. Waterfor these Jets is supplied from the usual mill supply througha flexible hose coupling and flow switch (not shown) to the nozzles 13 and It. Preferably these nozzles are located below the plane of the strip and are mounted on a carriage E5 in spaced apart relationship with each other to provide a narrow, neutral zone, e. g., a neutral zone of approximately 1 4;- inch between the two jets at the plane of the strip it. The

nozzles l3 and It direct the jet in proximity to the right edge iila of the' strip so that in normal operation when the edge of'the strip is stationary, the jet 5? will be projected past the edge of the strip, and the jet II will strike the strip and thus make electrical contact therewith. Preferably, the jets are arranged on the up-mill side of the apron plate of the mill so as to permit the scale from the strip to fall into the pit on the downmill side of the apron plate. The jets and the carriage are arranged within a protective enclosure (not shown) which is providedwith suitable openings through'which the jets are directed to the proximity of the edge of the strip.

As shown, the carriage I5 is mounted on a lead screw I6 which is driven by suitable driving means, such for example, as the electric motor ll, to the rotor of which the lead .screw is directly connected. Although the motor I! may be of any suitable type, it is preferably a direct The contacts 2la of aline contactor 2! are inthe primary winding 22b of cluded in the connections between the armature of the motor and the source 13.

Although the electric valves 19 and of any suitable type, they are preferably grid controlled, mercury vapor thyratron tubes, The

cathodes 19a and 20a of the valves 19 'and 20 which control the supply of current ,to the arma tures are indirectly heated, and these valves are provided with control grids- 19b and 20b,1respectively. As shown. electric valves 19 and 20 are connected "back to back, i.1-e.', the anode 29 maybe a part of the-millthrough whmh contact is com-.-

' battery is illustratedas valve 20, and the cathode 19a of valve I9 is connected 'to'the anode of-v'alve As thus connected," these valves'provide'ior supplying pulses of unidirectional current, of selected polarity to the armature of the motor l1 and therebyprosee r the control grid26c is" connected through resistors 32' and 33 to the negative terminal of a battery 34, and the cathode '26d.is1connected to a point 34am? the battery which is'positivev with respect) to the negative terminal and thus the grid-26c. withrespect to the volt is given a negativebias age of its cathode. A'mid-terminal 36b, of the nection' from; memmpdme 34b. be made to pleted t'otnfe strip-10a -'Ihe iu udn point are. be

1 tween resistors 32 and 33 connected by"? means of a conductor to .:the'nozzle 13, and thus when. the Jet-l l imakes 'contact'with. the strip ID, the controlgridj26c of=valve 26 is'connected through the jetjl li-strip-lmand conductor 36 to the midpoint-3400f the battery which is positive with respect to the point 340 of the battery to which the cathode 26a is connected. As a result the valve 26 will be rendered conducting.

tective resistor and the secondary winding 22a of a grid transformer to the cathode 19a. A source of biasing potential, such for example as a battery 23, is included in the connections between the cathode and the grid and serves to apply a negative bias to the grid. The grid 20b and cathode 20a of valve 20 are similarly-connected through a protective resistor, the secondary winding 24a of a grid transformer 24, and a biasing battery 25.

For the purpose of controlling the energization of valves 19 and 20, an additional pair of electric valves 26 and 21 is provided which are respectively connected in circuit with the primary windings 22b and 242:, respectively, of grid transformers 22 and 24. The primary windings 22b and 2411 are connected through supply transformers 28 and 29 to suitable sources of alternating voltage 30 and 3!, which sources may be and preferably are the same-source as the source 13.

Although the electric valves 26 and 21' may be of any'suitable type, they are" preferably grid controlled, mercury vapor thyratron tubes. The cathodes 26a and 21a of the valves 26 and 21 are indirectly heated. and these valves are provided with shield grids 26b and 2117 as well as with control grids 26c and 210, respectively. In thyratron valves. such as thevalves i9, 20, 26 and 21, the function of the control grid is only to initiate the flow of current betweenthe anode and cathode during each positive half-cycle of anode voltage. Once current has started to flow,

the grid exercises no further control until the conductivity of the valve has been interrupted by some means external to the valve itself. Once In a typical installatiom-the resistor 32 may have .a resistance of between 50,000 and 100,000 ohms,and the resistor 33 may have a resistance of twice the resistance of the jet H which in a typical installation may be between 200,000 and 600,000 ohms;

The resistor 33 and jet ll'con'stitute adjacent arms of abridge circuit between the cathode26a and the control grid 260 of valve 26, and similarly, the resistor 39 'and'jet l2 constitute adjacent arms of a similar bridge between the cathode 21a and the grid 21c of valve 21. The specific resistance of the water jets is subject to sudden changes which produce changes in the relationship of the voltage drops across the adjacent bridge arms of these bridges, which may be of sufilcient magnitude to cause false operation of the apparatus. For the purpose of avoiding such false operations, the resistors 33 and 39 mayeach be constituted of the flowing volume of water between two metal pipe'inserts 12 and 13 in a the current has ceased to flow, the voltage of the grid will again determine the point in the positive half-cycle of anode voltage at which the valve will again become conducting. These valves are therefore grid-controlled, arc rectifiers.

The anode-cathode circuit of electric valve 26 is traced from the upper terminal of the secondary winding of supply transformer 23 through the grid transformer 22 .to, the anode 26d of valve 26 and from the cathode 26a to the lower terminal of the secondary winding of transformer 23. As shown,

tube 16 of rubber, or' other' suitable insulating material through which the water flows to the associated jet as illustrated in Fig. 2. The pipe inserts 12 and 13 serve as terminals of the water resistor and are connected inthe circuits in the.

manner in which the terminals of the resistors 33 and 39 in Fig. lare connected.

Thus, the water which constitutes the resistors 33 and 39 immediately subsequently constitutes the jets II and 12. As a result the relationships of the voltages across the adjacent arms of the bridge circuits between the cathodes and grids of valves 26 and 21 remain unaffected by any change in the specific resistance of the' water constituting these arms. and thus false operation of the apparatus'onthis account is eliminated.

The anode-cathode circuit of the valve 21 is traced from the upper terminal of the secondary winding of supply transformer 29 through primary winding 2lbof grid transformer 24 tothe anode of the valve 21, and from the cathode through conductor 31. to the lower terminal of the secondary winding of supply transformer 29.

210 is biased positively with respect to the cathode, and the valve is normally conducting.

The resistances of resistors 33 and 39 are approximately equal to the resistances of resistors 32 and 33, respectively, andthe junction point being connected to the strip i0; However; in actual practice thelcone the jet driving motor .stator winding of the transmitter 50 are con- 380. of resistors 38 and 33 is connected by means of a conductor 30 to the nozzle M. Thus, when the jet i2 is in contact with the strip ill whichv .tive bias with respect to the cathode, and the valve will become non-conducting.

The apparatus thus far described constitutes a unit for detecting the position of the right edge illa of the strip. For the purpose of detecting the position of the left edge liib of the strip, a unit similar to the unit already described is provided. This unit comprises a' pair of nozzles 4| and 32 for directing a pair of jets 3 and 4'5 in proximity to the edge "lb of the strip, a motor 45 for rotating the lead screw 55 which drives the carriage 41 upon which the nozzles 5| and 42 are mounted, and an electric valve amplifier apparatus 58. The electric valve amplifying unit 48 is in all respects identical with the electric valve amplifying unit which is enclosed within the dotted rectangle 49, and therefore, the unit 48 is illustrated conventionally.

For the purpose of indicating the positions and changes in positions (5f the edges la and I?) of the strip and for indicating the width and variations in the width of the strip, electric motion transmitting devices 50, and 52 and an electric motion receiving device 53 are provided. The electric motion transmitting device 50 comprises a rotor member 500, which is provided with a single-phase alternating current winding (not shown) and a stator member 50b which is provided with a three-element distributed winding (not shown), which is physically similar to a polyphase winding. The rotor and stator windings of the device are in inductive relationship with each other. The single-phase rotor winding is energized from'a suitable source of single-phase alternating current voltage which is indicated in the drawing by the two supply lines 54. The electrical motion receiving device 53 is in all respects identical with the transmitting device 50, andthe single-phase rotor winding is connected to the source 54.

The transmitting device 5| has a rotor member 5|a which is provided with a distributed three-element winding (not shown) and a stator member 5|b which is also provided with a distributed three-element winding. The rotor and stator windings of this device are also in inductive relationship with each other. As indicated in the drawing, the electrical motion transmitting device 52 is in 'all respects identical with'the device 5|.

The rotor member 50a ,of the transmitter 5|) is connected through suitable gearing to the shaft of the-jet driving motor 45. and similarly, the rotor member of the transmitter 52 is connected through suitable gearing to the shaft of The terminals of the nected by means of conductors 55 to corresponding terminals of the stator windings of transmitter 5|, andsimilarly, the terminals of the stator windingof the transmitter 52 are connected by means of conductors 56 to corresponding terminals of the rotor winding of transniitting device 5|. Also, asshown, the terminals of the rotor winding of transmitting device 52 are connected to corresponding terminals of the stator winding of receiving device 53.

The motion transmitting and receiving devices 55, 5|, 52, and 53 are of the self-synchronous typeand thus have the following properties. If the rotors oi the devices 5| and 52 are restrained and the rotor of the transmitter 53 is rotated, the rotor of the receiving device 53 will faithfully reproduce the motion of the transmitting device 55. Likewise, if the rotors of the transmitters 5i] and 5B are restrained, and the rotor of the transmitting device 52 is rotated, the rotor of the receiving device 53 will reproduce the motion of the rotor of the transmitter 52. Similarly, if the rotor of the device 5| is restrained and the rotors of the transmitters and 52 are rotated, the rotor of the receiving device 53 will rotate an amount equal to the algebraic sum of the motions of the transmitters 50 and 52. In other words, the connections between the devices 50, 5|, 52, and 53 are so made initially that if the jet driving motors H and 45 are moving the jets either toward or away from each other, the receiving device 53 will rotate an amount in one direction or the other which is equal to the algebraic sum of the rotations of the transmitters 5|) and 52, whereas, if the motors H and 45 are moving both sets of jets in the same direction along the lead screws I6 and H (for example to the right), the rotor of the receiver 53 will rr ate an amount which is equal to the difference of the rotations of the transmitters 5|] and 52. Consequently, if the motors i1 and 45 rotate both sets of jets the same amount, there will be no difference and the rotor of the receiving device 53 will remain stationary.

For the purpose of deenergizing the control when no strip is in the mill, a sensative thyratron type amplifier 58 and relay are provided for controlling the energization of the operating coil of the contactor 2|. The input or grid circuit to the amplifier 58 is connected by means of conductors 58a and 58b to the strip l0 and to a nozzle 59 which directs a jet 60 against the lower surface of the strip l0. Power is supplied to the thyratron amplifier 58 from a suitable source of alternating voltage 6| which may be and preferably is the same source as the source which is indicated by the supply lines l8, When the strip I0 is in the mill in the'positionindicated, the input circuit to the amplifier 58 will be completed through the jet 60 and the operating coil of the contactor 2| will be energized, and the contacts 2|a and 2|b of the contactor will be closed to complete the armature connections of the jet driving motors l1 and 45 to thesource l8.

The rotor of the transmitting device 5| is connected through suitable gearing to an odometer type indicating device 62 which is calibrated in terms of width of the strip l0. Similarly, the receiving device 53 is provided with an indicating device comprising a movable indicating pointer 63 cooperating with a dial 64 which is graduated in fractions of an inch, on opposite sides of a central zero position. Initial, the indicating apparatus is setup and adjusted so that when the jets I2, and 43, 44 are correctly positioned on the edges of a strip of the width for which the dial 62 is set, the pointer 63 will indicate zero on the dial 64. a

With the foregoing understanding of the apparatus and its organization in the system, the operation of the system itself will readily be understood from the following detailed description. It will be assumed in this explanation that during the previous operation, a strip of 61 inches in width was passed through the mill,

and it will further be assumed that the next strip to be passed through the mill is 61 inches in width. The indicating device 62 is set by means of the knob 62a to read 61 inches.- Since the rotors of the transmitters 50 and 52 are restrained against rotation by means of the gearing', motors, lead screws, and carriages to which they are connected, rotation of the rotor of the transmitter 5i when the knob 62a is turned will cause the rotor of the receiving device 53 to rotate an amount equal to the rotation of the rotor 5m in setting the indicating device from 61 inches to 61- inches. Rotation of the receiving device 53will turn the indicating pointer 63 to a position such that when the jets II. I! and 43, 44 are moved in to the correct positions with respect to the edges of a fil-inch strip, the indicating, pointer 63 will be rotated back to the zero position in which it is illustrated. In other words; the indicating pointer 63 and dial 64 are zeroed for each width of strip by rotation of the knob 62a.

When the stripiii ofassumed width of 61 inches enters the mill, the input circuit to the ihyratron amplifier 56 is completed through the jet 60 and the strip and as a result, the contractor 2i closes its-contacts to connect the armatures of the jet moving motors i1 and45 to the source 16.

Since, on the previous pass, the jets ii and I2 were spaced Irom the jets 43 and 44 the correct amount for a 6l -inch strip, they will be too far apart for a 61-inch strip and in general, will occupy the positions with respect to the edges of the strip ii) that are illustrated in the drawlug. i. c. all four jets will be out of contact with the strip iii. Since the jet Ii is out of con tact with the. strip iii, the grid 260 of the valve 26 will be biased negatively with respect to its cathode and consequently valve 26 will be nonconductingf Onthe other hand. the grid 210 of Y, valve 21' which is connected to the positive terminal'oi' thebattery 34 will be biased positively withrespect to its cathode and the valve 21 will conduct positive-half-wave impulses. These'impulses will be t ansformed and supplied to the grid 20b of the valve 26 which will also conduct positive half-wave impulses and transmit them through thearmature of the motor I! in such a direction that the carriage i5 will be moved to the left, i. e.. inwardly ---toward ,thecenter line of thestrip Iii. In a similar manner, the motor "45 will'be caused to rotate in such a direction as to move the carriage 41 toward theright or inwardly toward the center line of the strip I6.

When the-carriage 15 has been moved suf-. .ficiently far to the'left to effect contact between v the jet Ii and the strip iii. the grid 26cof valve 26 willbe connected through the jet and strip I to the midpoint 34b of the battery 34, which point is positive with respect to the point 342! to which .the cathode of valve 26 is connected. and consequently. valve 26 will become conducting and this, in turn, will render the valve l9 conducting. However. since the valve l9 supplies current impulses to --the armature of the motor I i! in the opposite direction fromthat in which current is supplied by the valve 20', -no "torque" will-be developed and the motor will be dynamically braked to rest-with the jet ii in contact with the strip iii and the jet [2 out of contact with the strip l0. Similarly, the motor 45 will come to rest with the jet 44 in contact with the strip iii and the jet 43 out of contact with the 1 strip I6.

The motors I! and 46 in moving the jets il and I2 and 43 and 44 to their correct positions with respect to the edges Illa and "lb of the strip I I6 'rotate the rotors of the transmitters 56 and 52 corresponding amounts, and these transmit- I ters cause the rotor of the receiving device 66 to rotate the pointer 63 tothe zero position on the dial 64 when the jets are correctly positioned with respect to the strip. v

If at some point in the length of the strip II. the width should become less than 6! inches in such a manner that the right edge Ila of the strip moves out of contact with the jet ii, the positive bias is removed from the grid 26c of the valve 26 and this valve and'the valve i6 ceases conducting. However, the valve 21 and the valve 26 continue to conduct, and the motor i1 is energized in a direction to move the carriage II inwardly toward the *center line of the strip until the jet ii again makes'contact with the strip i0 atwhich time the valves 26 and I. again become conductingand'the motor ll is again brought to rest. The rotation of the motor 11 rotates the transmitter 52 a corresponding amount and the rotation of the transmitter 62.

is reproduced by the receiver 53-with the result that the indicating pointer 66 is moved to the left or minus side of the dial anamount corresponding to the movement of thejet Ii, and

therefore, an amount corresponding to the change in'position of the edgevlla of the strip.

Similarly, it the left edge lilb of the strip moves away from the jet 44, the motor 45 is energized to move the carriage 41 to the right until-contact is reestablished between the jet 44 and the strip Ill. The rotation of the motor 46 effects a corresponding rotation of the transmitter 56 and receiver 53 with the result that the indicating pointer 63 is moved to the left a corresponding amount. Thus, the position of the pointer 63 .with respect to the graduated dial 64 indicates the position of the left edge Nb of the strip. Actually, the 1 indicating pointer inmoving to the left indicates the amount of decrease in the.

width of the strip from 61 inches, and the rotation of'either the motor II or the motor 45 indicates which edge of the strip has moved away from the jet'with which it should be in contact.

If. the width of the strip 10 decreases in a manner such that both edges Ilia and 16b of the strip move away from the jets II and; both motors i I and 45 will be simultaneously energized and will move the jet inwardly until contact is reestablished, The motors I1 and 45 in moving the jets to their correct positionswill rotate both transmitters 50 and 52 simultaneously. *The receivingtdevice 53 will rotate an amount equalrto the algebraic sum of the rotation of the transmitters 50 and 52, and the indicating pointer 63 will be moved to the position on the graduated, scale which indicatesthe total decrease in the width of the strip.

If the strip increases in width in such ner that the right edge Illa of the .strip moves outwardly so that it is in contact with both jets ii and I2, the grid 210 of the valve-21 will be Y connected to the point 64b which is negative with respect to the point 340 to which'thecathode L 21a is connected, and consequently, the valve 21 I is rendered nonconducting. As a result, the valve 20 is also rendered nonconducting and ceases to supply current impulses to the'armature of the motor l'l. However, the valves 26 and is remain conducting and the valve l9 continues to supply current impulses to the motor I! in a direction such that the motor I? moves the carriage i outwardly to follow the edge of the strip. When the jet i2 is again moved out of contact with the strip iii, the negative bias is removed from the grid 21c of the valve 21, and the valves Z'iand 26 again become conducting and the valve 26 supplies current impulses to the armature of the motor ii in the opposite direction to that in which current is supplied from the valve 19, and consequently, the motor l1 again comes to rest. The rotation of the motor I! during this operation effects a corresponding rotation of the transmitter 52 and likewise a corresponding rotation of the rotor of the receiving device 53.

Since the rotation of the motor I? was in the opposite direction from that of its rotation when the width of the strip decreased, the indicating pointer 53 will be rotated to the right and the amount of its rotation will indicate the new position of the edge I-lla of the strip. If the amount of increase exceeds the amount of demay be provided. As indicated in the drawing, these units comprise motion receiving devices 66 and ti connected in parallel with motion receiving device 53, and associated indicating pointers and dials. Similarly, devices for indicating the strip width setting are provided at these stations. These devices comprise receiving devices 58 and 69 electrically connected to a transmitting device it the rotor of which is mechanically connected to the setting knob 62a. Odometer type indicating devices it and H are driven by receiv= ing devices 68 and 69, respectively.

Although in accordance .with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained, together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative crease previously described, the pointer 63 will be rotated to the right of the zero position.

If the left edge ifib of the strip moves outwardly, the result will be the same, i. e., the indicating pointer 63 will be moved to the right an amount corresponding to the change in position of the edge lb of .the strip.

If both edges Ilia and lflb of the strip moved outward simultaneously, the indicating pointer 63 is moved to the right an amount equal to the algebraic sum of the movements of both edges from their initial positions.

If the width of the strip remains constant but the strip itself should be laterally displaced, e. g., to the right, the jets will be correctly repositioned with respect to the edges of the strip in the manner described in the foregoing. In this case, however, the motor 45 will rotate in a direction opposite to that in which it rotated when the edge of the strip moved to the left, as described in the foregoing.

Indications should only be read when the stripedges are stationary. The condition of the appa-v ratus is an indication of the condition of the edge, e. g., if the edge is stationary, the jet positioning motor associated with such edge is 'stationary, and if the edge is moving, the motor is rotating. However, the motor is enclosed within a protective casing and thus the'operator is unable to observe whether it is rotating or stationone of the electrodes of each of the glow tubes 84 and 65 will glow. This condition indicates to the operator that the edgeis in motion and that a reading should not be taken. However, when the motors are stationary, current impulses of opposite polarity are supplied to the motors during successive half-cycles, and thus each electrode of the glow tubes is alternately positive and negative.

and both electrodes of each tube glow. This indi cates to the operator that the edge is stationary and that the reading may be taken.

Ifit is desired to transmit the indications to a plurality of remote indicating stations, additional indicating units located at such-remote stations and that the invention is not limited thereto,

since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a system for indicating the position of the edge of an object of electrical conducting material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past the edge of said object in predetermined initial positional relationship with respect thereto, means responsive to a change in the electrical conductivity between said jet and said object in response to a change in the position of said object for moving said jet to restore said initial positional relationship, and means for indicating the amount of said restoring movement.

2. In a system for indicating the position of the edge of an object of electrical conducting material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past the edge 'of said body and in predetermined positional relationship with respect thereto, means for moving said jet, means responsive to a change in the condition of conductivity between said jet and object following a change in the position of said edge with respect to said jet for actuating said moving means to move said jet-in a direction to restore said positional relationship and responsive to the restoration of said positional relationship for terminating said movement of said jet, and means responsive to said movement for indicating the amount thereof.

3. In a system'forindicating the position of the edge of an object of electrical conducting material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past .the edge of said object in predetermined initial positional relationship with respect thereto, driving means for moving said jet, an electric circuit including said'jet and said object, means connected to said circuit and responsive to a change in conductivity between said jet and said object following a change in position of said edge with respect to said jet for actuating said driving means-to move said jet in a direction to restore said initial positional relationship, and means responsive to the movement of said jet for indicating the amount of said movement.

4. In a system for indicating the position of a for moving said jet to a initial predeterminedvrelationship, and means.

' follow said changes in the positions .of said 1 moving said jets to edges, and means sum of the movements of said jets.

'7 object oi electrical prising .in combination,,means ior projecting a ,jet or electrical conducting fluid past each or; opposite edges of said object, means including a sumoifthe movements electrical motion receiving .tion transmitting devices and electrically connected an edge of an object of electrical conducting material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past the edge of said object and in predetermined initial positional relationship therewith, means including an electric motor responsive to a change in the electrical conductivity between said jet and said object in response to a change in position 01 said edge with respect to said jet for indicating the amount of movement oi said jet.

5. Inc. system for indicating the width oi an object of electrical conducting material thatis past each of opposite edges of said object in initial predetermined positions with respect to said edges, means responsive to changes in the I electrical conductivity between said jets and said object in response to changes in position of said edges for independently moving said jets to in position of said edges, and means for indicating the algebraic sum of assesses sum of saidmovements oi said jets to said reoeiving device and a device driven by said receiving device for indicating the amount of motion otsaid receiving device.

position to restore said 7 T subject. to movement in'the direction of its width, the combination projecting a jet of electrical conducting fluid comprising means for the movements of said jets irom'said initial positions.

6. In a system for indicating the width of an object of electrical conducting material that is subject to movement in the direction of its width, the combination comprising a mat means for projecting a jet of electrical conducting fluid past one edge of said object in initial predetermined position with respect to said edge, a second meansfor projecting a second jet or, electrical conducting fluid past the opposite edge of said object, means responsive to changes in the electrical conductivity between said jets and said object-in response to changes in the positions of said edges for independently moving said jets to new positions to follow the changes in positions or said edges, and means for indicating the algebraic sum of the movements of said jets from said initial positions.

'1. A system for indicating the width of an object of electrical conducting material comprising in combination, means ilor projecting a jet of electrical conducting fluid past each of oppositeedges of said object, means including a pair ofelectric motors separately responsive to changes in the electrical conductivity between said jets and said object in response to changes edges for independently follow the movements of said for indicating the algebraic 8. A sy'stemior' indicating the width of an conducting material compair oi electric motors separately responsive to changes inlthe electrical conductivity. between said jetsand said object in response to changes inthe'positions of said edges for independently moving said jets to "follow the movements of said edges, and means for indicating the algebraic of isaid jets comprising an to each other and to said receivingdevice to transmit thealgebraic 9: a device for indicating the position of the edge of an object or electrical conducting material comprising" in combination, means for projecting a flrst jet of electrical conducting 10. A device for indicating the position er theedge of an object of electrical conducting material comprising in combination, means for projecting a flrst jet of electrical conducting fluid past an edge or said object and for projecting a second jet oielectrical conducting fluid in contact with said object, means responsive to a movement of said edge out of contact with said second jet for moving both said jets to follow said edge and responsive to movement of said edge in'the opposite direction into contact with said first jet for moving both said jets in the opposite direction to follow the changes in position 01' said edge, and means for indicating the amount of movement of said jets.

11. A device for indicating the position of the edge of an object of electrical conducting material comprising in combination, means for projecting a jet oi. electrical conducting fluid into proximity with said edge, an electric .motor for moving said jet in the direction of the width of said 0bject.-electric valve means responsive to changes in the electrical conductivity between said jet and said object in response to changes in position of said edge for controlling said motor to move said jet to follow the changes in the position or said edge, and means driven by said motor for indicating the amount of movement 0! said jet;

12. A device for indicating the position or the edge. of an object oi! electrical conducting msterial comprising in combination, means for Pro- .Iecting a first jet oi'electrical conducting fluid into contact with said object and a second jet '0! electrical conducting material past said edge,

an electric motor for moving said jets and electric valve means responsive to contact of said object with both said jetsin response to changes of position in said edge in one direction for controlling said motor to move said jets to follow said edge-and responsive to interruption or contact between said jets and'said object in response to movement oi! said edge in the opposite direction for controlling said motor to move said device, electrical modriven-by said motors jets in said opposite direction to follow said edge. and means- !or indicating the amount'oi movement of said jets.

13. A'system for measuring the width oi an I object of electrical conducting material compris ing in combination,a first position indicating unit operatively associated with one edge or said object and a second position indicating unit operatively associated with the opposite edge oi said object, each of said unitscomprisirig means for projecting a pair of narrowly separated jets of electrical conducting fluid so that .one jet passes its associated edge of said object and the other jet makes contact with said object, -an electric motor for moving said jets and electric valve means responsive to contact of said object with both said jets in response to change of posi-,

- direction for controlling said motor to move said jets in said opposite direction to follow said edge, and means driven by the motors of both said units for indicating the algebraic sum of the movements of the jets of both said units.

14. A device for indicating the position of an edge of an object of electrical conducting material comprising in combination, means for projecting a jet of electrical conducting fluid in proximity to an edge of said object, an electric motor for moving said jet, means responsive to a change in the conductivity between said jet and said body in response to a change in position of said edge for controlling said motor to move said jet to follow the change in position of said edge, means for indicating the amount of movement of said jet, and mean for projecting a second jet into contact with an object which is in operative position with respect to said first jet, and means responsive to interruption of contact between said second jet and said object when said object moves out of operative relationship with said first jet for rendering said device inactive.

15. In a system for indicating the position of the edge of an object of electrical conductin material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past the edge of said object in predetermined initial positional relationship with respect thereto, means responsive to a change in the electrical conductivity between said jet and said object in response to .a change in the position of said object for moving said jet to restore said initial positional relationship, means for compensating for changes in the resistance of said jet produced by changes in the specific resistance of said fluid, and means for indicating the amount of said restoring movement.

16. In a system for indicating the position of the edge of an object of electrical conducting material subject to movement in the direction of its width, the combination comprising means for projecting a jet of electrical conducting fluid past the edge oi said object in predetermined initial positional relationship with respect thereto, driving means for moving said jet, a bridge circuit including said jet and object as one arm thereof and a resistor constituted of fluid flowing to said jet asan adjacent arm thereof for compensating for changes in the resistance of said jet produced by changes in the specific resistance of said-fluid, means connected to said circuit and responsive to a change in conductivity between said jet andsaid object following a change in position of said edge with respect to said jet. for actuating said driving means to move said jet in a direction to restore said initial positional relationship, and means responsive to the movement of said jet'for indicating the amount of said movement.

LOWELL L. HOLMES, JR. oaam w. uvmos'ron, 

